By the dozens they came to Kasr Al-Ayni Al-Qadima hospital on Monday to stretch out their arms and give blood in solidarity with fellow Cairenes demanding regime change in Egypt.
"We are here for our brothers on the street," said Hassan, a young man in his twenties, stretched out on a long bench in the blood bank at the university medical centre in the heart of the capital.
"It is the first time in my life that I have given blood," he said, blood trickling into a plastic bag for eventual transfusion to those injured in clashes between protesters and security forces.
Monday was day seven of an ongoing popular uprising against the longtime Egyptian president that has left at least 125 dead and several thousands injured in the Arab world's most populous nation.
"I have come here because there have been victims," said Rokayya, her face behind a veil, at the hospital not far from Tahrir Square, epicentre of the protests. "No one in my family has been hurt. I came spontaneously."
"I want to contribute positively to what is going on," agreed Bassem, a bearded young doctor also waiting his turn to give blood. "Breaking things is negative. Giving blood is positive."
In the wake of the most violent incidents on Friday, when police opened fire on the crowds, several hundred people started converging on Cairo hospitals to replenish their blood supplies.
"Many of the injured people lost a great amount of blood," said the hospital's director general, Ashraf Mahmoud Hatim, in whose vast office hangs a Mubarak portrait. "They need blood."
Since Saturday, he said, the blood bank has received 1,500 units a day - nearly four times the usual daily average of 400 units.
The families of the injured were among the first to give blood, but little publicity was needed to encourage others to come forward.
"We were reluctant to use our vehicles because some ambulances and some blood-bank vehicles from the ministry of health were hijacked by looters," Hatim told AFP.
"That is why we said: 'Anybody who wants to donate, please, come to us'."
Prominent among admissions to the hospital have been eye injuries among protesters who had been targeted with tear gas or rubber bullets to the face, the director general said.
"Usually, in normal conditions, we have two or three such cases in a day," he said. "This has been very difficult to deal with, because they must be operated on in the first 24 to 48 hours so as to regain sight and not lose vision."
By the end of Monday, donations had been so generous that the blood bank was full, and the hospital asked that would-be donors return in a couple of days.
"We are afraid that this thing will continue," Hatim said, wondering if his hospital might run out of bags for new blood.